Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 36 1 2001 Structure and Cohesive Energy of Large Spherical Coulomb Clusters 41 49 EN Hiroo Totsuji Tokunari Kishimoto Chieko Totsuji Kenji Tsuruta The ground state of spherical clusters of charged particles of one species confined by the three-dimensional parabolic potential is investigated by molecular dynamics simulations with the system size from N = 5000 to N = 1.2 × 10(5) . The cohesive energy per particle is compared between the shell-structured clusters and spherical finite bcc lattices with relaxed surfaces, the former and the latter being the ground states for small systems and for the large enough systems, respectively. It is shown that, when N > N(c)(N(c) > N), finite bcc lattices with relaxed surfaces (the shell structures) have stronger cohesion than the shell structures (finite bcc lattices with relaxed surfaces) and the critical value of the transition N(c) is estimated to be 10(4) < N(c) < 1.4 × 10(4) . The nucleation of the bcc lattice in the shell-structured cluster of 2 × 10(4) ions is observed. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 37 1 2002 Estimation of the screening length and the electric charge on particles in single-layered dusty plasma crystals 11 14 EN Chieko Totsuji Muhammad S. Limant Kenji Tsuruta Hiroo Totsuji A theoretical approach which has been successful in reproducing results of molecular-dynamics simulations on dusty plasmas is applied to estimate the screening length and the electric charge of two-dimensional dust crystals of melamine particles in the discharge chamber experiment. It has been found that the screening length is of the same order of magnitude as the inter-particle distance and the electric charge decreases on increasing number density of dust particles. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 38 1-2 2004 Dynamical Properties of Two-Dimensional Yukawa Liquids: A Molecular Dynamics Study 33 37 EN M. Sanusi Liman Chieko Totsuji Kenji Tsuruta Hiroo Totsuji The dynamic structure factor and the spectrum of the momentum-density fluctuations of 2D Yukawa liquids are analyzed in the domain of weak and intermediate coupling and screenlng parameters. The dispersion relations of the longitudinal and transverse collective excitations are obtained and compared with the random phase approximation (RPA) and harmonic approximation for triangular lattice. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 38 1-2 2004 Structure of Dusty Plasma under Microgravity 29 32 EN Hiroo Totsuji Chieko Totsuji Takafumi Ogawa Kenji Tsuruta The structure of dust particles in dusty plasmas under microgravity has been analyzed by molecular dynamics simulation. The charge neutrality condition satisfied by the system composed of dust particles and ambient plasma is properly taken into account. It is shown that dust particles form shell structures at low temperatures and the number of shells are obtained as a phase diagram in the plane of two parameters characterizing the system: the number of particles and the strength of screening. It is also shown that these structures are almost independent of the strength of screening. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 70 1 2004 Thermodynamics of a two-dimensional Yukawa fluid EN Hiroo Totsuji M. Sanusi Liman Chieko Totsuji Kenji Tsuruta Thermodynamic quantities of a two-dimensional Yukawa system, a model for various systems including single-layered dust particles observed in dusty plasmas, are obtained and expressed by simple interpolation formulas. In the domain of weak coupling, the analytical method based on the cluster expansion is applied and, in the domain of intermediate and strong coupling, numerical simulations are performed. Due to reduced dimensionality, the treatment based on the mean field fails at the short range and exact behavior of the binary correlation is to be taken into account even in the case of weak coupling. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 72 3 2005 Structure of spherical Yukawa clusters: A model for dust particles in dusty plasmas in an isotropic environment EN Hiroo Totsuji Takafumi Ogawa Chieko Totsuji Kenji Tsuruta The structure of spherical clusters composed of Yukawa particles is analyzed by molecular dynamics simulations and theoretical approaches as a model for dust particles in dusty plasmas in the isotropic environment. The latter condition is expected to be realized under microgravity or by active cancellation of the effect of gravity on the ground. It is found that, at low temperatures, Yukawa particles form spherical shells and, when scaled by the mean distance, the structure is almost independent of the strength of screening including the case of the Coulomb interaction. The positions and populations of shells and the conditions for the change of the number of shells are expressed by simple interpolation formulas. Shells have an approximately equal spacing close to that of triangular lattice planes in the bulk close-packed structures. It is shown that, when the cohesive energy in each shell is properly taken into account, the shell model reproduces the structure of spherical Yukawa clusters to a good accuracy. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 71 4 2005 Ordering of dust particles in dusty plasmas under microgravity EN Hiroo Totsuji Chieko Totsuji Takafumi Ogawa Kenji Tsuruta Structure formation of dust particles in dusty plasmas under microgravity has been simulated by the molecular dynamics method. It is shown that, at low temperatures, dust particles are organized into layered spherical shells. The number of shells is a function of the system size and the strength of screening by ambient plasma particles, while the dependency on the latter is much weaker. In the simulation, the condition of the charge neutrality satisfied by the system of dust particles and plasma particles is properly taken into account. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 44 2010 Numerical Simulation of Acoustic Waves in a Two-Dimensional Phononic Crystal: Negative Refraction 7 12 EN Kenji Tsuruta The lens effect of acoustic waves in a two-dimensional (2D) phononic crystal is studied by numerical simulation based on the finite-difference time-domain (FDTD) method. We calculate the phonon band structure of 2D phononic crystals, consisting of metal cylinders placed periodically in water. Lens effect is observed by the negative refraction of acoustic waves, which results in refocusing of the waves at the point outside the crystal. To increase the focal intensity, we introduce a 2D phononic crystal shield with a different composition of material, which returns the incident waves back to the lens via the perfect reflection. Also, the dependence on filling fraction of metal in the crystal is studied. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 44 2010 FDTD Analysis on Optical Connement Structure with Electromagnetic Metamaterial 1 6 EN Kenji Tsuruta In this paper, we investigate a light-confinement phenomenon in the structure which has triangular latice composed of Double NeGative Metamaterial (DNGM). In geometrical optics consideration, this structure is expected to confine lights completely by sequential refractions in the structure. We demonstrate it by using the two dimensional finite-difference time-domain simulations. We introduce Drude-Lorentz model for dielectric and magnetic dispersion of the material at optical frequencies. We analyze quantitatively the effects of energy loss in the DNGM on the light-confinement efficiency. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 33 2 1999 O(N) Tight-Binding Algorithm for Large-Scale Molecular Dynamics Simulations 71 77 EN Kenji Tsuruta Hiroo Totsuji Chieko Totsuji A parallel tight-binding molecular dynamics with an order-N [O(N))] algorithm is implemented to perform large-scale simulation of nanostructured materials. The algorithm is based on the Fermi-operator expansion of an electronic energy and force, and we present its basic formalisms. Accuracy necessary for molecular-dynamics simulations can be obtained by a proper truncation in the expansion. Parallel efficiency on a parallel PC cluster shows nearly ideal scaling behavior with respect to the number of processors. Applicability of the method to a silicon-carbide system is examined. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 33 2 1999 Multicomponent Plasmas in Penning-Malmberg Traps 61 69 EN Hiroo Totsuji Kenji Tsuruta Chieko Totsuji The behavior of multicomponent plasmas in the Penning-Malmberg traps is discussed with the parameters corresponding to experiments with antiprotons and cryogenic electrons. The relaxation times for the energy transfer antiprotons to electrons and between parallel and perpendicular components of electrons are estimated. It is shown that, depending on the values of parameters, both the former and the latter can be the bottleneck in the cooling process. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 33 2 1999 Density Functional Molecular Dynamics of Hydrogen Plasma 51 59 EN Hiroo Totsuji Kenji Tsuruta Chieko Totsuji Density functional molecular dynamics method is applied to hydrogen plasma in the domain of liquid metallic hydrogen. Tentative results for the proton-proton pair distribution function and the electron-proton pair distribution function are obtained. It is shown that with the increase of the parameter γ(s), we have increasingly strong screening of proton charge by electrons and the decrease of electron density in the domain between protons. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 43 2009 Information Transfer and Entanglement Creation by Spin Chains: Effects of Noise and Asymmetry 22 26 EN Hiroo Totsuji Chieko Totsuji Kenji Tsuruta For the transfer of quantum information and the creation of entangled states, the application of tuned spin chains, systems of spins with the nearest-neighbor coupling tuned so as to give high efficiency, has been proposed and some examples of high performance have been given by several authors. In this article, the effect of deviations from tuned values and the effect of resultant asymmetry are investigated through numerical simulations and theoretical analyses. It is shown that there exists a system where the transfer efficiency is comparable with exactly tuned ones and, at the same time, robust to noises in the coupling constants. It is also shown that the effect of asymmetry on the efficiency of entanglement creation is of the second order when the asymmetry is small. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 43 2009 FDTD Simulations of Acoustic Waves in Two-Dimensional Phononic Crystals using Parallel Computer 16 21 EN Kenji Tsuruta Chieko Totsuji Hiroo Totsuji The finite-difference time-domain (FDTD) method has been applied to the calculation of the phonon band structure of two-dimensional (2D) phononic crystals, consisting of metal cylinders placed periodically in liquid. By comparing several combinations of materials for metal cylinder and liquid, we analyze the dependence of the band structures on sound speed and density of liquid media. Moreover, the negative refraction of the acoustic waves is observed at the interfaces between phononic crystal slab and the liquid. We find that an acoustic“lens effect”with the slab appears due to the negative refractions. The relationship between the focal intensity in the lens effect and the band structure is discussed. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 43 2009 Dispersion Models and Electromagnetic FDTD Analyses of Nanostructured Metamaterials using Parallel Computer 8 15 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji Metamaterial which has negative permittivity and permeability is investigated via computer simulations. Effects of the nanostructure on dielectric and magnetic properties of the material are taken into account by introducing the Drude-Lorentz model in the materials dispersion. We include multi-band process in the dielectric response in order to reproduce accurately experimental values of bulk Au thin film. Size effect on the dispersion is examined by comparing the model with that of a noble metal particle. Based on the dispersion model constructed, we analyze the electromagnetic response of nanostructured metamaterials to evanescent waves at microwave and optical frequencies via finite-difference time-domain simulatioins on parallel computer. A re- focusing and an amplification of the evanescent waves propagating through a metamaterial, consisting of metal slab/vacuum stacking, is demonstrated for the frequencies of 30GHz and 744THz. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 35 1-2 2001 Molecular Dynamics of Yukawa System using the Fast Multipole Method 77 95 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji In order to perform the large-scale molecular dynamics simulation of the Yukawa system, a mathematical expression for molecular dynamics using the fast multipole method is described. The model simulations are also performed to test the performance of our implementation of the FMM. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 35 1-2 2001 Nonorthogonal Tight-Binding Molecular Dynamics for Si(1-x)Ge(x) Alloys 63 75 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji We present a theoretical study of Si(1-x)Ge(x) alloys based on tight-binding molecular dynamics (TBMD) calculations. First, we introduce a new set of nonorthogonal tight-binding parameters for silicon and germanium based on the previous work by Menon and Subbaswamy [Phys. Rev. B 55, 9231 (1997); J. Phys: Condens. Matter 10, 10991 (1998)]. We then apply the method to structural analyses of Si(1-x)Ge(x) alloys. The equilibrium volume and atomic structure for a given x are obtained by the TBMD method. We also calculate the bulk modulus B, elastic constants C(11), C(12) and C(44) as a function of x. The results show that the moduli vary monotonically, but nonlinearly, between the values of Si crystal and Ge crystal. The validity of the results is also discussed. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 39 1 2005 Large-Scale Molecular Dynamics Simulation of Coulomb Clusters: A Finite-Temperature Analysis 52 55 EN Katsuya Kanamori Chieko Totsuji Kenji Tsuruta Hiroo Totsuji Thermal behavior of Coulomb clusters in a three dimensional confining potential is investigated by molecular dynamics simulations for system sizes of 1,000 to 20,288 ions. The specific heat of the system of shell-structured 20,000 ions is peaked almost at the same temperature as the system of bcc-structured 20,288 ions with much sharper structure for the latter. The diffusion coefficient and the peak to valley ratio of the two-dimensional pair distribution function on the outermost shell are obtained both as a function of temperature. The rotational movement of each shell in the system of 104 ions is observed. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 39 1 2005 Electron Dynamics in Semiconducting Nanowires: A Real-Space, Polynomial-Expansion Approach 46 51 EN Keisuke Kadono Chieko Totsuji Kenji Tsuruta Hiroo Totsuji We present a real-space, polynomial-expansion approach to electron dynamics in nanostructured semiconductors. The Chebyshev expansion method is employed for efficient calculation of timeevolution of single-electron wave function. Details of the formulation are described. The method is applied to the electron transport in nanostructured semiconductors such as Si nanowires. The mean-square displacement and diffusivity of electron in Si chains are obtained as functions of length of the chains. The results show clearly ballistic behavior of electron in the pure Si chain. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 40 1 2006 Distribution of Electrons in Quantum Dots Analyzed by Classical Mapping and Molecular Dynamics 40 43 EN Miyake Takashi Chieko Totsuji Kenji Tsuruta Hiroo Totsuji The electron system of arbitrary degeneracy can be mapped onto a classical system where electrons of the same spin are assigned an additional interaction and the effect of degeneracy is taken into account through an imaginative temperature. We apply this method to electrons in quantum dots modeled as two-dimensional electron liquid confined in a finite domain by a harmonic potential. We analyze distribution functions by molecular dynamics instead of solving integral equations which are not so useful in the case without translational invariance. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 40 1 2006 Stochastic-Dierence-Equation Method for Long Time-scale Molecular Dynamics Simulations 36 39 EN Atsushi Uchida Chieko Totsuji Kenji Tsuruta Hiroo Totsuji We present a Stochastic-Difference-Equation (SDE) approach to long time-scale molecular dynamics (MD) simulations, which are required for nanosecond-scale phenomena. In this method, the MD trajectory in a fixed time period is obtained as a stationary solution of an action functional based on an error accumulation of the equation of motion along the path, thus reducing the problem to a boundary-value problem, instead of an initial-value problem in the ordinary MD method. We apply the method to formation processes of Cu thin film via nanocluster deposition onto a substrate. The applicability of the SDE algorithm to the problem and the effects of the choice of SDE parameters on the optimization processes of configuration pathway are examined. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 40 1 2006 Melting of Spherical Yukawa Clusters Analyzed by Monte Carlo Simulation 31 35 EN Takafumi Ogawa Chieko Totsuji Kenji Tsuruta Hiroo Totsuji We analyze the melting of spherical Yukawa clusters by Monte Carlo simulations. Spherical clusters are expected to be found in dusty plasmas in an isotropic environment such as microgravity and serve as a model for classical clusters. We obtain the specific heat through fluctuations of the potential energy and identify its peak as the transition temperature. Melting temperatures are compared with those of bulk Yukawa systems and it is confirmed that the melting temperature increases and approaches the bulk value with the increase of the system size. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 42 1 2008 Spin Polarization of Two-Dimensional Electron System in a Finite Domain 56 59 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji We analyze the ground state of the two-dimensional quantum system of electrons confined in a parabolic potential with the system size around 100. We map the system onto a classical system on the basis of the classical-map hypernetted-chain (CHNC) method which has been proven to work in the integral-equation-based analyses of uniform unbounded systems and then apply classical numerical simulations. We find that the confined system undergoes the transition to the spin polarized state with the decrease of the average density and the corresponding critical value is as low as rs ∼ 0.3 in terms of the usual rs parameter estimated for the average density. As the ground state for given value of the rs parameter, our data give the critical value for the transition around 20 which is consistent with the known possibility. The advantage of our method is a direct applicability to geometrically complex systems which are difficult to analyze by integral equations. The application to the structure like quantum dots reported here is the first example of such applications. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 42 1 2008 Numerical Simulations of Two-dimensional Electron Fluid : An Application of Classical-map Hypernetted-chain Method 48 52 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji Based on the mapping introduced by the classical-map hypernetted-chain (CHNC) method, classical numerical simulations, Monte Carlo and molecular dynamics, have been applied to the twodimensional electron fluid and the results are compared with those of quantum Monte Carlo simulations hitherto reported. It is shown that polarization properties of the ground state obtained by the diffusion Monte Carlo method are reproduced within the accuracy of quantum simulations by both of two mapping functions for the quantum temperature which have been proposed within the CHNC method. These results may serve as the basis of numerical simulations based on the CHNC method which are applicable to finite non-periodic systems like quantum dots and systems at finite temperatures. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 42 1 2008 Vibrational Properties of Si Crystal with Vacancy : A Tight-Binding Study 44 47 EN Kenji Tsuruta Chieko Totsuji Hiroo Totsuji To analyze vibrational properties of Si crystal with a single charge-neutral vacancy, we perform large-scale simulations based on tight-binding molecular-dynamics method. Vibrational modes and frequencies are obtained by diagonalizing dynamical matrix within a harmonic approximation. Results indicate that there exist vibrational modes spatially localized around the vacancy and large frequency shifts associated with the localized modes contribute significantly to reduction of the vibrational free energy. No potential conflict of interest relevant to this article was reported.